Dopper shift increases with ionospheric disturbance and the solar geophysical reports always show that the effect is more pronounced in northern latitudes. I don't know a lot about the physics of the ionosphere but I assume that it's for the same reason the aurora always occurs near the poles. My information comes from measurements summarized in published papers.
73, John KD6OZH ----- Original Message ----- From: cesco12342000 To: digitalradio@yahoogroups.com Sent: Thursday, November 30, 2006 03:45 UTC Subject: [digitalradio] Re: USA: No Advanced Digital HF Data Comms > Near the equator, > there is little frequency spread (< 4 Hz), but it is larger > in near-polar paths and can be very large (up to 40 Hz) > under disturbed conditions. A question: where does the frequency spread come from ? Is this a doppler effect of a moving ionosphere, or are there other causes ? why is the effect bigger in polar regions ?
